Internal combustion engines use recirculated exhaust gas to reduce emissions of nitrogen oxides (NOx). Achieving the optimum combination of air and burnt gasses within the engine cylinder prior to the start of combustion on each engine cycle may not be possible due to the dynamics of the air system. To address this problem, control strategies are used to attempt to regulate the intake manifold pressure and the percentage of exhaust gas recirculation (EGR). Traditional engine control strategies use open loop tables and/or proportional-integral-derivative (PID) controllers. These systems tend to have errors under transient conditions because the open loop tables are calibrated for steady state conditions and the closed loop PID controls depend on sensor feedback, which inherently has lag. A physics-based feed forward calculation can be used instead of the open loop tables and PID controls. The feed forward calculation can provide better response under transient conditions, prioritize control objectives, account for system constraints, and be easier to calibrate.
Some engine control systems use an EGR flow Venturi or other flow sensor to estimate an EGR mass flow rate. These flow sensors can be expensive, can be unreliable and can cause additional warranty cost. If other sensors can be used to provide similar performance it may be possible to reduce cost and improve reliability.
It would be desirable to have engine control systems and methods that can estimate EGR mass flow rates using other sensors instead of an EGR flow Venturi or other types of flow sensors.